The present invention relates to a totally-enclosed type motor and, in particular, to a totally-enclosed type motor having an interior cooling passage system, in which cooling air circulated by an interior fan passes through an inside ventilation passage of a stator frame, and an exterior cooling passage system, in which cooling air provided by an exterior fan passes through an outside ventilation passage of the stator frame.
The general structure of a conventional totally-enclosed type motor is shown in FIG. 4A and FIG. 4B. As shown in FIG. 4A and FIG. 4B, the conventional totally-enclosed type motor structure is roughly constituted by a rotor shaft 101, a rotor core 107 having a rotor winding 108, and a stator core 105, which is arranged around the outside of the rotor core 107, is separated therefrom by an air gap 110 and has a stator winding 106. The conventional totally-enclosed type motor structure is roughly constituted further by two bearing members 102 for rotatively supporting the rotor shaft 101, two bracket members 103 for closing the axial ends of the stator frame 104, an exterior fan 112 which is arranged on the shaft 101 outside of the bracket member 103, and an end covering member 113 for covering the exterior fan 112.
With a conventional totally-enclosed type motor of the above stated construction, almost all heat loss, which is generated in the stator core 105, the stator winding 106, the rotor core 107 and the rotor winding 108, is heat-transferred to the stator frame 104 through the stator core 105 by heat conduction. Further, as a result of a fan operation produced by an end portion of the rotor winding 108, as shown by a dotted line arrow in FIG. 4A, the interior air is agitated and heat is transferred to an inner face of the stator frame 104 and an inner face of the bracket member 103 through heat conduction. Therefore, a part of the heat loss is heat-transferred to the stator frame 104 through heat conduction. The heat being heat-transferred to the stator frame 104 is heat-radiated toward the outside of the motor and is conducted away by the exterior cooling air flow, as shown with a solid line arrow in FIG. 4A, produced by the exterior fan 112.
Another structure of a conventional totally-enclosed type motor is shown in FIG. 5A and FIG. 5B, and such a totally-enclosed type motor is disclosed, for example, in Japanese utility model laid open No. 88,454/1987. The totally-enclosed type motor structure shown in FIG. 5A and FIG. 5B differs from the totally-enclosed type motor shown in FIG. 4A and FIG. 4B in the following points.
The stator frame 104 of this totally-enclosed type motor structure has plural inside ventilation passages 104a, plural outside ventilation passages 104b, and an interior fan 109. The inside ventilation passages 104a are formed by the inside surface of the stator frame 104 and are spaced with a predetermined interval in the peripheral direction, as seen in FIG. 5B, and extend continuously in the axial direction, as seen in FIG. 5A. The outside ventilation passages 104b are provided on an outside surface of the stator frame 104 and extend continuously in the axial direction and are spaced in the peripheral direction between adjacent inside ventilation passages 104a, as seen in FIG. 5B. The interior fan 109 is arranged in the stator frame 104, so that by rotating the fan 109 together with the rotor shaft 101, the interior cooling air, which has cooled the stator core 105 and the rotor core 107, is sent out and is circulated through the inside ventilation passages 104a.
Two flows of cooling air are produced in the totally-enclosed type motor structure as shown by the arrows in FIG. 5A. First of all, the interior cooling air flow, which has been produced by the interior fan 109, as shown with dotted line arrows in FIG. 5A, passes through the inside ventilation passages 104a which are formed at the inner face of the stator frame 104. After that, the interior cooling air is distributed and passed through the air gap 110 and axial ducts 111. The interior cooling air then is returned again to the interior fan 109 and is continuously circulated.
Further, the exterior cooling air flow, as shown by solid line arrows in FIG. 5A, is drawn into an air inlet port 113a, which is provided on the end covering member 113 by the exterior fan 112. The exterior cooling air passes through the outside ventilation passages 104b, which are provided at an outside portion of the stator frame 104, and is then discharged to the outside.
A further conventional totally-enclosed type motor structure is disclosed in, for example, Japanese utility model laid-open No. 113,562/1989. This conventional totally-enclosed type motor structure is shown in FIG. 6A, FIG. 6B and FIG. 6C.
In the totally-enclosed type motor structure shown in FIG. 6A, FIG. 6B and FIG. 6C, the motor has no exterior fan, in contrast to the above stated former totally-enclosed type motor structures. In place of the exterior fan, in the totally-enclosed type motor structure shown in FIG. 6A, FIG. 6B and FIG. 6C, one end of a heat pipe 115 is projected toward and into the interior of the inside ventilation passage 104a. Plural heat radiation fins 117 are provided on the heat pipe 115 and are arranged on opposite sides of the inner projected heat pipe 115 so as to extend toward the outside of the inside ventilation passage 104a of the heat pipe 115 or outside of an outer frame 116. With the above stated totally-enclosed type motor structure, as shown in FIG. 6A, FIG. 6B and FIG. 6C, an enlargement of the heat-receiving area is attained by the provision of the heat pipe 115 having plural heat radiation fins 117.
In the conventional totally-enclosed type motor structure shown in FIG. 4A and FIG. 4B, since the interior cooling air is merely agitated, the amount of heat radiation is extremely small. As one example, the amount of heat radiation produced by the agitation is about 12% of the total heat radiation as one calculation example. Thus, the conventional totally-enclosed type motor structure shown in FIG. 4A and FIG. 4B has a defect in that there is a serious limitation on the heat transfer amount possible with this construction.
Further, in the conventional totally-enclosed type motor structure shown in FIG. 5A and FIG. 5B, the motor has two paths along which heat is transferred to the stator frame 104, these two paths providing for heat conduction (A) from the stator core 105 and heat transfer (B) due to the interior cooling air flow. The temperature rise in the motor is influenced by the total heat transfer resulting from the amount of the above stated heat conduction (A) added to the amount of the above stated heat transfer (B). For example, the heat conduction (A) can be made large by increasing the area of contact of the stator core 105 and the stator frame 104, however the heat transfer amount due to the heat transfer (B) will be small as a result. On the other hand, the heat transfer (B) can be made large by increasing the size of the inside ventilation passage 104a or the number thereof, however the heat transfer amount due to the heat conduction (A) will be made small as a result. Accordingly, the conventional totally-enclosed type motor structure shown in FIG. 5A and FIG. 5B has a defect in that there is a serious limitation on the heat transfer amount in the motor having such a construction.
Further, in the conventional totally-enclosed type motor structure shown in FIG. 6A, FIG. 6B and FIG. 6C, the heat radiation fins 117 are mounted on one side of the heat pipe 115 and are formed at the outside of the stator frame 104. The pitch in the axial direction of the arrangement of the heat pipes 115 is at least more than an outer diameter of the heat radiation fins 117, therefore there is a serious limitation on any increase in the heat-receiving area in the motor having this construction. Further, since there is no cooling fan provided outside of the stator frame 104, the heat removal is caused only by natural heat radiation, and therefore, there is a serious limitation on the heat transfer in the motor having this construction.